Field of the Invention
The invention relates to a method for detecting edges in an image signal.
In image processing, in particular television signal processing, the detection of edges is necessary for quite a number of digital signal processing methods. Edge detection is for example used for object recognition, for motion estimation, for eliminating flicker, or for improving the image quality by, for example, carrying out edge crispening or noise reduction. The quality of these signal processing methods depends to a large extent on the performance of the edge detection in the edge detector. It is in particular desirable to detect the edges with as much noise immunity as possible and with as much positional accuracy as possible.
Conventional edge detectors in television signal processing operate according to the principle of gradient formation. For this purpose, a sudden change in brightness in an image is determined basically by a difference formation. In the Laplace method, the second derivative of the gradient is used. Furthermore, different combinations of these methods are possible. If appropriate, convolution operations and weighting operations in longitudinally different directions can be included in these methods. The increased noise sensitivity on account of the difference formation is problematic in these methods. The edges determined may be more than one pixel wide, which leads to positional inaccuracies. There is no efficient determination of edges at masking locations. The formation of derivatives means that a high computation effort is necessary, and wide edges likewise lead to an increased computation effort.